28.输入两个链表，找出它们的第一个公共结点。

题目描述

输入两个链表，找出它们的第一个公共结点。

解题思路：先求两个链表的长度，决定让哪一个链表先走，然后在判断节点是否相等；

/*
public class ListNode {
int val;
ListNode next = null;

ListNode(int val) {
this.val = val;
}
}*/
public class Solution {
public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
if(pHead1==null||pHead2==null){
return null;
}
int count1 = 0;
ListNode p1 = pHead1;
while(p1!=null){
p1 = p1.next;
count1++;
}
int count2 = 0;
ListNode p2 = pHead2;
while(p2!=null){
p2 = p2.next;
count2++;
}
int flag = count1 - count2;
if(flag>0){
while(flag>0){
pHead1 = pHead1.next;
flag--;
}
while(pHead1!=pHead2){
pHead1 = pHead1.next;
pHead2 = pHead2.next;
}
return pHead1;
}
if(flag<=0){
while(flag<0){
pHead2 = pHead2.next;
flag++;
}
while(pHead1!=pHead2){
pHead2 = pHead2.next;
pHead1 = pHead1.next;
}
return pHead2;
}
return null;
}
}